WASHINGTON — Timothy F. Geithner was sworn in as secretary of the Treasury on Monday evening, confirmed by a Senate majority that concluded that his experience in government and finance outweighed concerns about recent disclosures of some $34,000 in past tax delinquencies.

The vote was 60 to 34.

The tax controversy had delayed Mr. Geithner’s confirmation, keeping him from taking office right after Barack Obama’s inauguration last Tuesday as administration officials had hoped, given the economic emergency.

In a desultory two-hour Senate debate on Monday, opponents cited the tax issue to explain their votes against Mr. Geithner’s leading the Treasury, which oversees the Internal Revenue Service. A couple of populist senators objected as well to the leading role he played, as president of the Federal Reserve Bank of New York, in government bailouts of financial institutions over the last few months. As early as next week, the new secretary will announce changes for the bailout program that are expected to press banks to make more loans and reduce housing foreclosures.

Mr. Geithner, 47, who was sworn into office by Vice President Joseph R. Biden Jr. in a ceremony at the Treasury Building attended by Mr. Obama, spent the first 13 of his 20 years in government service working for the Treasury, rising to under secretary for international affairs in the Clinton administration.

His confirmation became unexpectedly complicated this month by the disclosure that he failed to pay Social Security and Medicare taxes for 2001-4, when he was a senior official at the International Monetary Fund. As an international organization, the I.M.F. does not withhold taxes for American employees, though it does provide statements of their estimated liabilities and pays them an amount equal to the employer share of payroll taxes.

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Mr. Geithner ultimately paid a total of more than $48,000 in back taxes and interest, making one payment after an I.R.S. audit in 2006 and the rest last November. Privately and at his confirmation hearing last week before the Finance Committee, he apologized to senators for what he called an innocent mistake.

Senator Orrin G. Hatch of Utah, one of 10 Republicans to vote for Mr. Geithner, praised his credentials on the floor Monday, though he said Democrats would probably not have shown the same deference toward a Republican president’s nominee with similar violations.

Three Democrats — Senators Robert C. Byrd of West Virginia, Russ Feingold of Wisconsin and Tom Harkin of Iowa — voted against the nominee, as did an independent who caucuses with the Democrats, Senator Bernard Sanders of Vermont.

In a floor speech, Mr. Harkin said, “How can Mr. Geithner speak with any credibility and authority as America’s chief tax enforcement officer?”